QUANTUM-TRAJECTORY PICTURES OF LASER COOLING

We have applied the method of single-atom trajectories to study the me chanism behind some cooling schemes in laser cooling. In several cases we recognize the cooling mechanism as being due to a Sisyphus process , in which the atoms move in a spatially varying light-shift potential and are optically pumped toward the most light-shifted states. In oth er cases we identify a Sisyphus process in time, in which the light sh ift is constant and the force on the atom alternates between positive and negative. This process is interrupted by quantum jumps at random i nstants, and in each case we depict the mechanism leading to a cooling force on the atom. In the special case of sub-Doppler laser cooling i n a strong magnetic field we obtain 12 jump operators and identify the jump operators responsible for the cooling. The versatility of the si ngle-atom trajectory method permits it to be applied to any cooling pr ocess, and therefore it is a valuable tool in unraveling the physical mechanisms behind cooling processes.